In a generally accepted definition, an autonomous vehicle is a wheeled transportation device that can operate on conventional roads with little or no human intervention. The Society of Automotive Engineers (SAE) and the National Highway Traffic Safety Administration recognize six (6) levels of automation from SAE Level 0, in which the vehicle issues warnings to the driver and may momentarily intervene but has no sustained vehicle control, to SAE Level 5, in which no human intervention is required.
Multilane roads run the gamut from: undivided three-lane roads with at-grade crossings and property access along the shoulder (where the middle, or third, lane is used for cross traffic entrance and exit to the travel lanes); to controlled-access highways, in which opposite directions of travel are divided by a physical barrier such as a median or wall, ingress and egress are through ramps, and at-grade crossings are not present.